1. Field of the Invention
This invention relates to a personal watercraft, and particularly to an improved engine control system for a personal watercraft.
2. Description of the Related Art
Personal watercraft have become popular in recent years. This type of watercraft is sporting in nature and carries a rider and possibly one or more passengers. A relatively small hull of the personal watercraft commonly defines a rider's area above an engine compartment. An internal combustion engine frequently powers a jet propulsion unit that propels the watercraft. The engine lies within the engine compartment in front of a tunnel (e.g., a recess) formed on the underside of the watercraft hull. The jet propulsion is located within the tunnel and is driven by a driveshaft. The driveshaft usually extends between the engine and the jet propulsion device through a wall of the hull tunnel.
Personal watercraft often are operated in a planing state at wide open throttle. In a planning state, the hull of the personal watercraft supports the weight of a watercraft by planing or “skipping” over the surface of the water. However, if the speed of the personal watercraft suddenly decreases, the planing hull typically begins to “dig” into the water, and drag on the hull significantly increases. If the speed of the watercraft continues to drop, the watercraft hull will experience less and less planing support, and will eventually essentially operate as a displacement-type hull and the speed of the watercraft will be significantly reduced. Personal watercraft usually begin to plane at engine speeds of approximately 2000-3500 RPM.
While planing, it is not uncommon for the personal watercraft to jump out of the water. When this occurs, the engine speed suddenly increases because the hull is no longer substantially affected by water resistance. If this occurs, the engine speed can exceed a maximum value. This is generally undesirable and can result in damage to engine of the personal watercraft. As such, some personal watercraft include engine speed or “rev” limiting arrangements. In such arrangements, the engine speed is reduced when an engine speed sensor indicates that the engine is operating at an engine speed greater than the maximum value.
Personal watercraft are commonly powered by two-cycle engines, which have the advantage of being fairly powerful and relatively light and compact. However, two-cycle engines typically produce exhaust gases with relatively large quantities of carbon monoxide and various hydrocarbons. To reduce these emissions, personal watercraft typically include an exhaust system with a catalyst for cleaning the exhaust gases. One disadvantage of using a catalyst in a personal watercraft is that if the exhaust gases exceed a maximum temperature (e.g., 1000° C.), the catalyst can be damaged and/or the effectiveness of the catalyst is impaired. Such high exhaust gas temperatures can occur when the personal watercraft is planing for long periods at wide open throttle or if the engine speed suddenly increases such as when the watercraft jumps out of the water as described above.